A compressor of a gas turbine engine comprises rotor components, including rotor blades and a rotor drum, and stator components, including stator vanes and a stator casing. The compressor is arranged about a rotational axis with a number of alternating rotor blade and stator vane stages as is well known and each stage comprises an aerofoil. The efficiency of the compressor is influenced by the running clearances or radial tip gap between its rotor and stator components. The radial gap or clearance between the rotor blades and stator casing and between the stator vanes and the rotor drum is set to be as small as possible to minimise over tip leakage of working gases, but sufficiently large to avoid significant rubbing that can damage components.
The pressure difference between a pressure side and a suction side of the aerofoil causes the working gas to leak through the tip gap. This flow of working gas or over-tip leakage generates aerodynamic losses due to its viscous interaction within the tip gap and with the mainstream working gas flow particularly on exit from the tip gap. This viscous interaction causes loss of efficiency of the compressor stage and subsequently reducing the efficiency of the gas turbine engine.
EP 2 378 075 A1 discloses a turbine blade having a tip that carries winglets which project laterally from the turbine blade at the radially outer end of the suction surface and pressure surface respectively. A gutter is formed in the winglet's tip and the position and direction of the gutter exit provides control over mixing losses associated with the return of gases from the gutter to the main working gas flow.
EP 1 013 878 B1 discloses a turbine blade including an airfoil having pressure and suction sidewalls joined together at leading and trailing edges and extending from a root to a tip plate. Twin ribs extend outwardly from the tip plate between the leading and trailing edges and are spaced laterally apart to define an open-top tip channel therebetween. Each of the tip ribs has an airfoil profile for extracting energy from combustion gases flowable around the turbine blade. The pressure side tip rib is stepped away from the main airfoil pressure surface and extends from the leading edge of the airfoil.
However, two main components to the over tip leakage flow have been identified. A first component that originates near a leading edge of the aerofoil at the tip and which forms a tip leakage vortex and a second component that is created by leakage flow passing over the tip from the pressure side to the suction side. This second component exits the tip gap and feeds into the tip leakage vortex thereby creating still further aerodynamic losses.
The turbine blade winglet configuration of EP 2 378 075 A1 aims to prevent the formation of the tip leakage vortex by virtue of the winglets overhanging the pressure and suction surfaces and the winglet being present at the leading edge of the aerofoil.
The tip rib configuration of EP 1 013 878 B1 aims to extract work from the main working gas flow by diverting a portion of the working gas flow into its channel and turning the flow from the leading edge to the trailing edge. The presence of the pressure side rib at the leading edge also aims to prevent the formation of the tip leakage vortex.